The present disclosure relates to processes of preparing hybrid toner compositions with toner particles having a core-shell type structure, where the shell contains a non-volatile (i.e., a low VOC (volatile organic compound)) coalescent agent. More particularly, embodiments herein relate to processes of preparing styrene acrylate hybrid toner compositions.
Hybrid toners having some of the polyester resin latex replaced by a styrene/acrylate latex is a key in facilitating future cost reduction for certain toner products. For example, hybrid toners may contain a styrene/acrylate shell and a core comprising a styrene-acrylate copolymer and amorphous polyester. By replacing the polyester with more styrene/acrylate copolymer, the cost is reduced as polyester is traditionally a more expensive material. Not only are the polyester raw materials generally more expensive, but to prepare polyester latex to enable use in emulsion-aggregation toner requires an additional processing step, which often requires the use of solvents, verses styrene/acrylate copolymers can be directly prepared as a latex when the resin is prepared by emulsion polymerization. However, the process of preparing these hybrid toners is challenging because the preparation of the styrene/acrylate shell requires higher temperature for coalescence compared to the polyester in the core. For example, a polyester emulsion/aggregation toner prepared by a batch process is generally coalesced at temperatures from about 70° C. to about 85° C., while a styrene/acrylate toner is generally coalesced at temperatures above 90° C., typically from 95 to 96° C.
A potential approach to address this mismatch is to elevate the coalescence temperature in the emulsion aggregation process to that typical from styrene/acrylates of about 95 to 96° C. However, depending on the Tg values of the styrene acrylate latex used in the shell, even with elevating the coalescence temperature may not be sufficient to enable a complete coalescence which leads to rough surface morphology of the toner particles, or may cause a loss of control of the toner particles during coalescence process resulting in poor particle properties, such as, toner particle size, toner particle shape, geometric size distribution (GSD), fines and coarse, as well as rejection of the styrene/acrylate latex, or rejection of other components, such as wax or pigment.
Thus, there exists a need to improve the coalescence of the styrene-acrylate to prepare hybrid toner particles. The inventors of the present disclosure discovered that by including a low VOC (volatile organic compound) coalescent agent in the toner shells can improve coalescence of the styrene-acrylate.